Methods of three dimensional (3d) airflow sensing and analysis

ABSTRACT

Embodiments of methods and apparatus for close formation flight are provided herein. In some embodiments, a method of sensing three dimensional (3D) airflow by an aircraft includes: collecting measurements characterizing airflow near the aircraft; analyzing the collected measurements; creating, by a processor, a computer model predicting one or more 3D airflow patterns parameter values based on the analyzing; obtaining one or more additional measurements characterizing airflow near an aircraft of the plurality of aircraft, and evaluating an error between an airflow parameter value predicted by the computer model and the one or more additional measurement.

FIELD

Embodiments of the present invention generally relate to methods andapparatus for close formation flight, and in particular for flightcontrol for organizing and maintaining close formation flight.Non-limiting examples include providing sensing capabilities and flightcontrol algorithms for maintaining relative aircraft positions withinthe formation that optimize flight performance.

BACKGROUND

Formation flight can be described as an arrangement of two or moreaircraft flying together in a fixed pattern as a cohesive group.Different types of aircraft regularly can be flown in formation. Oneexample of a formation flight is aerial refueling, where a receiveraircraft flies behind and below a tanker aircraft. In some of theseformations, the aircraft are sufficiently close to one another thattheir wakes affect the aerodynamic characteristics of each other. Thissituation is sometimes referred to as “close formation flight”.

Close formation flight is attractive because of its potential tosignificantly reduce the aerodynamic drag and increase lift for theaircraft in formation. These effects in turn can lower power requiredfor propulsion, reduce fuel consumption, and increase aircraftendurance, flight range, and payload.

While there are definite aerodynamic benefits of such formation flight,it has not been used in practice so far due to difficulties in flightcontrol in close formation. Furthermore, the close proximity of theaircraft presents an unacceptably high risk of collision for mostapplications.

Close formation flight can be used for aerodynamic drag reduction, witha follower aircraft flying in the upwash generated by a leader aircraft.However, it has been very difficult for pilots on piloted aircraft andautopilots on unmanned airborne vehicles (UAV) to maintain properpositions in the formation for extended periods of time. In both cases,manned and unmanned aircraft, special automated control systems arerequired. Such systems must be able to determine relative locations ofthe aircraft and their trailing vortices to a very high degree ofaccuracy, in order to produce and sustain a close formation.

Wake turbulence is typically generated in the form of vortices trailingbehind aircraft wing tips and other lifting surfaces. The pair ofvortices generated by each aircraft is the result of lift beinggenerated by the wings and air rotating around the wingtips from thehigh pressure regions at the bottom of the wing to the low pressureregions at the top of the wing.

Generally, these vortices are considered dangerous to other aircraft,particularly to those positioned directly behind within the waketurbulence. The wingtip vortices generated by a leading aircrafttypically negatively affect the flight of trailing aircraft, bydisrupting its aerodynamics, flight control capabilities and potentiallydamaging the aircraft or its cargo and injuring the crew. This makesmanual flight control in close formation very difficult and challenging.As a result, conventional autopilot systems prevent close formationflight, by avoiding areas with wake turbulence.

Therefore, the inventors believe there is a need for an advancedadaptive flight control system with capabilities to provide reliable andaccurate onboard flight control for aircraft in close formations. Such asystem would enable multiple aircraft, both manned and unmanned, toproduce and maintain close formation flight for extended time and thusachieve substantial benefits in aerodynamics performance outlined above.

Proposed solutions for such a system so far have been limited in theiraccuracy and efficacy. Some flight control systems are equipped toestimate the position of wingtip vortices trailing a leading aircraft,and control the flight characteristics of trailing aircraft to avoid thevortices. The position of a wingtip vortex relative to a trailingaircraft is estimated based on the flight characteristics of the leadingaircraft and an estimate of the wind generated by the trailing aircraft.

Proposed close formation flight systems, as a rule, do not account forthe effects of winds and drift on the wingtip vortices. The wingtipvortices, however, may move under the influence of winds and shift theirposition unpredictably between the leading and trailing aircraft.Because wingtip vortices cannot be directly visualized, the uncertaintyin their position makes close formation flight not only challenging, butoften impossible.

Older systems for formation flight control typically implemented agradient peak-seeking approach to move the objects relative to eachother to maximize or minimize a desired metric, i.e., fuel consumption.This approach uses a dither signal to determine a change in relativeposition to improve the metric. The change is effected, the resultsanalyzed, and the position further updated once again using a dithersignal to continually improve the metric. This gradient approach topeak-seeking may eventually position the aircraft close to the desiredrelative position in an ideal situation. However, such an approach issluggish, time-consuming and unresponsive, so that in fast-changingconditions it becomes ineffective.

Some conventional formation flight control systems attempt to estimatethe position of a wingtip vortex and control the position of a trailingaircraft relative to the estimated position. An inaccurate estimate ofthe vortex position leads to inaccurate relative positioning of theaircraft in formation. In addition, existing formation flight controlsystems fail to adequately account for vortex-induced aerodynamiceffects acting on the aircraft.

Thus, the inventors have provided embodiments of improved apparatus,systems, and methods for close formation flight.

SUMMARY

Embodiments of methods and apparatus for close formation flight areprovided herein. In some embodiments, a method of sensing threedimensional (3D) airflow by an aircraft includes: collectingmeasurements characterizing airflow near the aircraft; analyzing thecollected measurements; creating, by a processor, a computer modelpredicting one or more 3D airflow patterns parameter values based on theanalyzing; obtaining one or more additional measurements characterizingairflow near an aircraft of the plurality of aircraft, and evaluating anerror between an airflow parameter value predicted by the computer modeland the one or more additional measurement.

In some embodiments, a method of searching for an airflow patternincludes: defining a target search area relative to an aircraft;establishing a dithering flight pattern intersecting with the targetarea; collecting measurements characterizing airflow near the aircraft;analyzing the collected measurements; and determining a location of anairflow pattern based on the analyzing.

In some embodiments, a method of vortex tracking by an aircraftincludes: receiving airflow data from an airflow sensor on the aircraft;analyzing the airflow data by an onboard processor; mapping at least apart of the vortex field by the onboard processor; identifying thelocation of a vortex core; and measuring the position of the vortex corewith respect to the aircraft.

Other and further embodiments of the present invention are describedbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention, briefly summarized above anddiscussed in greater detail below, can be understood by reference to theillustrative embodiments of the invention depicted in the appendeddrawings. It is to be noted, however, that the appended drawingsillustrate only typical embodiments of this invention and are thereforenot to be considered limiting of its scope, for the invention may admitto other equally effective embodiments.

FIG. 1 depicts an exemplary close flight formation, in which severalfixed-wing aircraft are staggered behind each other, in accordance withat least some embodiments of the present invention.

FIG. 2 depicts an exemplary close flight formation, in which multipleaircraft form a V-pattern, in accordance with at least some embodimentsof the present invention.

FIG. 3 depicts an exemplary close flight formation, in which twoaircraft have one wing each aligned with respect to a wing of the otheralong the streamwise direction, in accordance with at least someembodiments of the present invention.

FIG. 4 depicts a spanwise separation along the Y axis in a dualformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 5 depicts a vertical separation along the Z axis in a dualformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 6 shows a horseshoe vortex model used to describe the wake behind afixed-wing aircraft in accordance with at least some embodiments of thepresent invention.

FIG. 7 shows a dual aircraft close formation in accordance with at leastsome embodiments of the present invention.

FIG. 8 shows a triple aircraft close formation in accordance with atleast some embodiments of the present invention.

FIG. 9 shows a larger close formation in accordance with at least someembodiments of the present invention.

FIG. 10 shows the vortices of FIG. 6 in a different view plane.

FIG. 11 shows a single vortex in the Y-Z plane propagating along the Xaxis (flight direction).

FIGS. 12-13 respectively depict the variation of magnitudes of vortextangential velocity components V_(y) and V_(z) for a wingtip vortex as afunction of position in the Y-Z plane plotted in the reference frameshown in FIG. 10.

FIG. 14 depicts variations of wingtip vortices resulting in a shift inexpected position of the vortices

FIG. 15 shows a method of vortex sensing in accordance with at leastsome embodiments of the present invention.

FIG. 16 shows a method for airflow vortex searching in accordance withat least some embodiments of the present invention.

FIG. 17 shows a method of vortex tracking in accordance with at leastsome embodiments of the present invention.

FIG. 18 shows a method of vortex recovery in accordance with at leastsome embodiments of the present invention.

FIG. 19 shows a method of forming a close formation for a group flightbetween two aircraft in accordance with at least some embodiments of thepresent invention.

FIG. 20 shows a method of forming a close formation for a group flightbetween more than two aircraft in accordance with at least someembodiments of the present invention.

FIG. 21 shows a method of preliminary and initial handshaking between atleast two aircraft in accordance with at least some embodiments of thepresent invention.

FIG. 22 shows a method of coarse alignment between two aircraft for aclose formation flight in accordance with at least some embodiments ofthe present invention.

FIG. 23 shows a method of fine aligning between two aircraft for a closeformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 24 shows a method of close formation optimization in accordancewith at least some embodiments of the present invention.

FIG. 25 shows an exemplary fixed-wing aircraft configurable for a closeformation flight in accordance with at least some embodiments of thepresent invention.

FIG. 26 shows the flight control architecture for a group of aircraft ina close formation fleet in accordance with at least some embodiments ofthe present invention.

FIG. 27 shows an aircraft equipped with a series of airflow sensorsmounted on various components of the aircraft in accordance with atleast some embodiments of the present invention.

FIG. 28 shows an aircraft that may be equipped with at least two typesof airflow sensors which may be positioned on different parts orlocations of the airframe in accordance with at least some embodimentsof the present invention.

FIG. 29 shows a dual close formation consisting of two aircraft inaccordance with at least some embodiments of the present invention.

FIG. 30 shows an airflow sensing system, in which an aircraft hasairflow sensors mounted at two special locations of the wing inaccordance with at least some embodiments of the present invention.

FIG. 31 shows a graph of the vertical air velocity V_(Z) produced by aneye sensor versus the lateral (spanwise) displacement of the vortex Ywith respect to the eye sensor.

FIG. 32 shows a cross-section of a Pitot tube used for air speedmeasurements in accordance with at least some embodiments of the presentinvention, in which there are two air channels.

FIG. 33 shows a specialized airflow probe in accordance with at leastsome embodiments of the present invention which may be used to measureV_(Y) and V_(Z) components.

FIG. 34 shows input ports of a specialized airflow probe aligned eitherin the vertical direction or in the horizontal direction (or in anyother plane if required) in accordance with at least some embodiments ofthe present invention.

FIG. 35 shows a specialized airflow sensor in accordance with at leastsome embodiments of the present invention which may be used to measureair flow speed and direction.

FIG. 36 shows a specialized airflow probe head in accordance with atleast some embodiments of the present invention which may be used forair flow measurements.

FIG. 37 shows another specialized airflow probe head in accordance withat least some embodiments of the present invention which may be used forair flow measurements

FIG. 38 shows a specialized airflow probe head in accordance with atleast some embodiments of the present invention which may be used forair flow measurements

FIG. 39 shows another specialized airflow probe head in accordance withat least some embodiments of the present invention which may be used forair flow measurements

FIG. 40 shows a three-dimensional view of a specialized airflow probehead in accordance with at least some embodiments of the presentinvention.

FIG. 41 shows a three-dimensional view of another specialized airflowprobe head in accordance with at least some embodiments of the presentinvention.

FIG. 42 shows a three-dimensional view of another specialized airflowprobe head in accordance with at least some embodiments of the presentinvention

FIG. 43 shows cross-sections of airflow probe heads in the planeperpendicular to the probe streamwise direction (e.g., X axis) inaccordance with at least some embodiments of the present invention.

FIG. 44 shows an airflow probe comprising an array of airflow probeheads in accordance with at least some embodiments of the presentinvention.

FIG. 45 shows a three-dimensional view of an airflow probe in accordancewith at least some embodiments of the present invention.

FIG. 46 shows a three-dimensional view of another airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 47 shows a three-dimensional view of another airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 48 shows a three-dimensional view of another airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 49 shows airflow sensor array system in accordance with at leastsome embodiments of the present invention in which a plurality ofairflow sensors are mounted on a wing.

FIG. 50 shows an airflow sensor system in accordance with at least someembodiments of the present invention, which may be used for airflowcharacterization and vortex sensing.

FIG. 51 shows an alternative airflow probe in accordance with at leastsome embodiments of the present invention.

FIG. 52 shows another vane-based airflow probe in accordance with atleast some embodiments of the present invention.

FIG. 53 further illustrates the working principle of the vane-basedairflow probe by showing a cross-section of a vane airflow probe inaccordance with at least some embodiments of the present invention.

FIG. 54 shows alternative airflow probe based on a hot wire principle,in accordance with at least some embodiments of the present invention.

FIG. 55 shows an alternative airflow sensor based on a hot wireprinciple, in accordance with at least some embodiments of the presentinvention.

FIG. 56 shows another alternative airflow sensor based on a hot filmprinciple, in accordance with at least some embodiments of the presentinvention,

FIG. 57 shows cross-sections of two orthogonal hot film probes, inaccordance with at least some embodiments of the present invention.

FIG. 58 shows a free-space optics approach, in accordance with at leastsome embodiments of the present invention, in which a leader aircraft isequipped with an optical source to produce a light beam at one of thewingtips along the streamwise direction towards a follower aircraft.

FIG. 59 shows another approach in accordance with at least someembodiments of the present invention that may facilitate vortexsearching and coarse aligning for a close formation.

FIG. 60 shows another approach that may facilitate close formationflight in accordance with at least some embodiments of the presentinvention.

FIG. 61 shows a method of sensing three dimensional airflow by anaircraft in accordance with at least some embodiments of the presentinvention.

FIG. 62 shows a method of searching for an airflow pattern by anaircraft in accordance with at least some embodiments of the presentinvention.

FIG. 63 shows a method of vortex tracking by an aircraft in accordancewith at least some embodiments of the present invention.

FIG. 64 shows a method of operating aircraft for flight in closeformation in accordance with at least some embodiments of the presentinvention.

FIG. 65 shows a method of operating aircraft in a close formation flightin accordance within one or more embodiments of the present invention.

FIG. 66 shows a method of changing positions of at least two aircraft ina close formation flight in accordance with one or more embodiments ofthe present invention.

FIG. 67 shows a method for metric evaluation of a close formationbetween a leader aircraft and a follower aircraft.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. The figures are not drawn to scale and may be simplifiedfor clarity. It is contemplated that elements and features of oneembodiment may be beneficially incorporated in other embodiments withoutfurther recitation.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of exemplaryembodiments or other examples described herein. However, it will beunderstood that these embodiments and examples may be practiced withoutthe specific details. In other instances, well-known methods,procedures, components, and/or circuits have not been described indetail, so as not to obscure the following description. Further, theembodiments disclosed are for exemplary purposes only and otherembodiments may be employed in lieu of, or in combination with, theembodiments disclosed.

In accordance with embodiments of the present invention, methods andapparatus for producing and maintaining a close formation flight withmultiple aircraft are provided. Aircraft in close formation typicallyfly together as a group in close proximity of each other and at the sameair speed. FIG. 1 shows for example an echelon formation 100, in whichseveral fixed-wing aircraft 110 may be staggered behind each other. Manyother formation patterns are possible: FIG. 2 shows another example of aclose formation, in which multiple aircraft 210 form a V-pattern 200.The simplest close formation 300 shown in FIG. 3 can be produced by twoaircraft 310 and 320, in which the left wingtip of the leader aircraft310 and the follower aircraft 320 are aligned behind each other alongthe streamwise direction 315. The defining characteristic of a closeformation flight in the context of this invention is that the positionof a follower aircraft should overlap with the streamwise projection ofa leader aircraft. Thus, the two aircraft may be physically separated bya relatively large distance 325, they may still be considered in a closeformation as long as this distance is shorter than the persistencelength of a wingtip vortex (or the vortex decay distance) produced bythe leader and this vortex can interact with the wingtip of thefollower.

The alignment between aircraft in a close formation may be characterizedby their tip-to-tip separation along the three axes (directions): Xaxis—the streamwise direction, Y axis—the spanwise direction and Zaxis—the vertical direction. FIG. 3 illustrates streamwise separation(distance 325) along the X axis. FIG. 4 shows spanwise separation 425along the Y axis between an aircraft 410 and an aircraft 420 in a dualformation 400. Similarly, FIG. 5 shows vertical separation 525 along theZ axis between an aircraft 510 and an aircraft 520 in a dual formation500. While the X distance in a close formation may be relatively large(ranging between 1 and 100 wingspans), the Y and Z distances should berelatively small, i.e., less than a single wing span or a fraction of awingspan.

The tolerance to misalignment between aircraft in a close formation isdetermined by the characteristics of wingtip vortices. Different modelshave been used to describe and visualize these vortices. FIG. 6 shows ahorseshoe vortex model 600 typically used to describe the wake behind afixed-wing aircraft. In accordance with this model, plane 610 with wing615 produces a pair of vortices 620 originating from the wingtips. Onthe outside of vortices 620 there are areas of upwash 630, whereas onthe inside of vortices 620 there is an area of downwash 640. Upwash 630may reduce the drag and increase the lift of the follower aircraft.However, downwash 640 may do the opposite—reduce the lift and increasethe drag. In this model we neglect the vortices produced by othersurfaces on the aircraft, e.g., on the tail or fuselage. In addition,other more complex computer models may be used to describe vortices,such as for example a vortex lattice method, which may be more accuratethan the horseshoe vortex model.

FIG. 10 shows these vortices in a different view plane 1000. Wing 1015of aircraft 1010 produces two wingtip vortices 1020 and 1030, where theright-hand vortex has a clockwise rotation and the left-hand vortex hasa counterclockwise rotation. As result, the air on the outer side of thevortices has an upward velocity component (upwash) and the air on theinside of the vortices has a downward velocity component (downwash).

FIG. 11 shows a vortex field 1100 having a single vortex in the Y-Zplane propagating along the X axis (flight direction). Particles in thisvortex are subjected to circular motion around the vortex core at thecenter of the coordinate system of FIG. 11. For example, particle 1110has a tangential velocity V with corresponding V_(y) and V_(z)components along the Y and Z axis, respectively.

If the vortex tangential velocity components V_(y) and V_(z) for vortex1030 (depicted in FIG. 10) are plotted in the reference frame of viewplane 1000 of aircraft 1010, their magnitudes (plotted on the verticalaxes) would vary as functions of position in the Y-Z plane as shown inFIGS. 12 and 13, respectively. For example, FIG. 12 depicts a plot 1200of the magnitude of vortex tangential velocity component V_(y) (on thevertical axis) as a function of position along the Z axis. Similarly,FIG. 13 depicts a plot 1300 of the magnitude of vortex tangentialvelocity component V_(z) (on the vertical axis) as a function ofposition along the Y axis. Both components are close to zero near thevortex core (i.e., the vortex core center) and have opposite signs onopposite sides of the core. The vortex core position in this coordinateframe is approximately at y=½ (one-half of a wingspan) and z=0.

FIG. 7 shows a dual aircraft close formation 700 composed of twoaircraft 710 and 750. The leader aircraft 710 generates vortices 720 andareas of upwash 730 and downwash 740. In order to achieve the mostbeneficial formation flight configuration, aircraft 750 should maximizethe overlap of its wing with the upwash area 730 and minimize theoverlap with the downwash area 740. The aircraft 710 and 750 may be ofthe same model type, but this need not be so. As such, the aircraft 710and 750 may have the same vortex, upwash and downwash generatingcharacteristics, or they may be dissimilar with respect to any or all ofthose characteristics.

Similarly, FIG. 8 shows a triple aircraft close formation 800 composedof three aircraft 810, 850, and 860. Because the leader aircraft 810generates wingtip vortices 820 and upwash areas 830 on both sides of thewing, two follower aircraft 850 and 860 may take aerodynamicallybeneficial positions behind the leader 810. In this case they may form aV-shaped close formation, in which the X distance between the leader andthe followers is in the range of a fraction of a wingspan to fewwingspans (less than 10). However, an extended close formation ispossible too, where at least one of the follower aircraft is separatedby an X distance of more than several wingspans (e.g., more than 10 andless than 100).

Larger close formation may comprise a greater number of aircraft, asshown in FIG. 9. Close formation 900 is a V-formation, comprising atleast 5 aircraft —910, 920, 930, 940, and 950 with corresponding wakeareas 915, 925, 935, 945, and 955 (each wake area having correspondingupwash and downwash areas as discussed above). In this case, someaircraft may play the roles of both leaders and followers, e.g.,aircraft 920 and 930 (both of which follow aircraft 910, and both ofwhich lead other aircraft following them). The most beneficial positionfor each aircraft in this formation is also determined by the bestoverlap of the follower's wing area with the leader wake's upwash area.This typically implies a close tip-to-tip positioning in the Y-Z planebetween any given leader-follower pair, i.e., a minimal separation inthe Y and Z directions. The above description is valid for closeformations in combination with different types of fixed wing aircraft,so that different types of aircraft may fly in the same formation andexperience the same or similar aerodynamic benefits.

The wingtip vortices usually do not stay in the same place, and insteadchange their position as shown in formation 1400 in FIG. 14. Information 1400, the leader aircraft 1410 may produce a pair of vortices1420, which subsequently will be subjected to interactions betweenthemselves, interactions with other vortices, atmospheric turbulence,winds, drafts, and the like. As a result, vortices 1420 may experience ashift from their expected position by a walk-off distance 1425, causingfollower aircraft 1450 to miss the vortices and thus fail to produce aclose formation. In addition, the size of the vortices may change too.The uncertainty in the vortex position and size may be reduced byreducing the X distance between the leader and the follower. However,this also significantly increases the risk of collision, reducesalignment tolerances between aircraft in the formation and makesformation flight control much more difficult.

Instead of estimating vortex positions from an indirect analysis ofvarious data, a better approach is to sense the vortices directly andbase formation flight control procedures on the real measurements of thevortex positions, rather than their estimates and predictions.

In accordance with embodiments of the present invention, a method 1500of vortex sensing (shown in FIG. 15) is provided in which the followingmay be implemented by the follower aircraft, either manually,automatically or both: measuring and collecting data at 1510characterizing airflow near the aircraft, analyzing the collected dataat 1520, creating a computer model of a vortex field at 1530, andevaluation of errors or differences between the model and the realvortex field at 1540. These processes may be repeated until the value oferror is below the acceptable limit or within the measurementuncertainty. The resulting model produces a set of static and dynamicparameters that simulate the airflow vector velocity field and itsdynamic behavior. In general, the model may simulate difference airflowpatterns and behaviors. In particular, it may simulate a single vortex,multiple vortices and vortex sheets. A simpler model (e.g., a singlevortex model) may be less precise than a more complex (e.g., a vortexsheet model), but easier to process and faster to implement. As aresult, a horseshoe vortex model shown in FIG. 6 or even a simpler modelof a single wingtip vortex may be well suited for the purposes ofin-flight vortex sensing, simulation and analysis.

The computer vortex model may produce a vortex field similar to vortexfield 1100 in FIG. 11. Instead of a complete vortex model, a simplifiedvortex model may be produced, in which only the vortex core andparticularly its center position (an eye position) is characterized. Therelative position of a vortex eye may be the primary parameter affectingthe flight control during the close formation flight. In somesituations, a complete or even partial vortex model may be difficult toproduce due to insufficient or noisy airflow data. However, it is stillmay be possible to provide sufficient information about the relativevortex eye location, e.g., whether it is on the starboard or port sideof the plane or whether it is above or below the plane.

Furthermore, additional processes may include one or more of varying Yand Z positions of the aircraft (either leader or follower), filteringand averaging airflow data provided by the measurements, using Kalmanfilters for data analysis and vortex model building, using complementarydata to create and refine the vortex model (e.g., data provided by otheraircraft in the same formation), and the like. Changing the aircraftposition in the direction suggested by the vortex model may bring theaircraft closer to the vortex eye, improve data collection and analysisdue to higher signal-to-noise ratio and improve the vortex model.Different vortex models may be used in different relative positionsbetween the aircraft and the vortex, e.g., a simpler less accurate modelmay be used when the separation between the vortex core and the aircraftis relatively large (e.g., larger than half of a wingspan).

In accordance with embodiments of the present invention, a method 1600for airflow vortex searching (shown in FIG. 16) is provided in which thefollowing may be implemented by an aircraft (e.g., the followeraircraft), either manually, automatically or both: defining the targetsearch area in XYZ space around the aircraft at 1610, establishing adithering flight pattern at 1620, in which the aircraft maysystematically fly through a grid of different X, Y, and Z coordinates,and continuous vortex sensing at 1630 until sufficient data is collectedto create a robust vortex model. A robust vortex model may be defined asa model produced by a set of real-time measurements, in which at leastsome of its characteristic parameters (i.e., vortex core diameter,position, strength, etc.) have converged to stable values. A flightcontrol system may specify the accuracy or precision required for vortexidentification, which then would determine the time when the vortexsearch may be considered completed. For example, positional accuracy inthe Y and Z directions may be specified as 5% of the wingspan.Additional processes may include one or more of communicating andexchanging telemetry data with other aircraft in the vicinity(particularly with the leader aircraft), using global positioning (GPS)data for narrowing the search area, using visual and other complimentarydata for narrowing the search area, using neural network and deeplearning algorithms for vortex patterns recognition, and the like. Thesearch area in the method may be limited to the scan within a YZcoordinate plane at a fixed X position with respect to the leaderaircraft.

In accordance with embodiments of the present invention, a method 1700of vortex tracking (shown in FIG. 17) is provided in which the followingmay be implemented by the follower aircraft, either manually,automatically or both: receiving continuously updated data of theairflow at 1710, analyzing the airflow data at 1720, mapping at least apart of the vortex field at 1730, identifying the location of a vortexcore at 1740 (particularly its center), and continuously orintermittently updating the position of the vortex core with respect tothe aircraft at 1750. Additional processes may include one or more offiltering and averaging airflow data provided by the measurements, usingKalman filters for data analysis and vortex model building, analysis andidentification of the vortex core, using complementary data to createand refine the vortex model (e.g., data provided by other aircraft inthe same formation), and the like.

In accordance with embodiments of the present invention, a method ofmultiple vortex tracking by an aircraft is provided in which thefollowing may be implemented by the follower aircraft, either manually,automatically or both: receiving continuously updated data of theairflow around the aircraft (e.g., at 1710) using onboard sensors,analyzing the received data creating computer vortex models (e.g., at1720), mapping the vortex field, subdividing the mapped vortex fieldinto different vortex regions (e.g, at 1730), identifying the locationof respective vortex cores and particularly their centers, andcontinuously or intermittently updating the positions of the vortexcores with respect to the aircraft. Additional processes may include oneor more of filtering and averaging airflow data provided by themeasurements, using Kalman filters for data analysis and vortex modelbuilding, analysis and identification of the vortex cores, using neuralnetwork and deep learning algorithms for vortex pattern recognition,using complementary data to create and refine the vortex models (e.g.,data provided by other aircraft in the same formation), and the like.

In accordance with embodiments of the present invention, a method 1800of vortex recovery (shown in FIG. 18) is provided in which the followingmay be implemented by the follower aircraft, either manually,automatically or both: preserving the computer model of the vortex fieldacquired by the aircraft at 1810, initiating the vortex search at 1820,reacquiring the vortex pattern at 1830, and updating the computer modelof the vortex and providing continuous updates for the vortexcharacteristics at 1840. Additional processes may include one or more ofusing neural network processing and deep learning algorithms for vortexpattern recognition, using complementary data to create and refine thevortex models (e.g., data provided by other aircraft in the sameformation), and the like.

In accordance with embodiments of the present invention, a method 1900of forming a close formation for a group flight between two aircraft(shown in FIG. 19) is provided in which the following may be implementedby the two aircraft, either manually, automatically or both: initialhandshaking between the aircraft at 1910, coarse aligning of theirrelative positions at 1920, vortex searching and tracking at 1930, andfine aligning of aircraft positions at 1940. Additional processes mayinclude one or more of establishing communication channel(s) and dataexchange network(s) between the aircraft, choosing one or more formationflight metrics and evaluating its parameters, optimizing relativeaircraft positions to maximize formation flight benefits by maximizingthe metric parameters, and the like.

In accordance with embodiments of the present invention, a method 2000of forming a close formation for a group flight between more than twoaircraft (shown in FIG. 20) is provided in which the following may beimplemented by the aircraft, either manually, automatically or both:forming a two-aircraft formation at 2010 (as outlined above), selectinga formation pattern for additional aircraft at 2020, adding at least oneadditional aircraft to the formation at the selected positions at 2030.Optionally, at 2040, 2030 may be repeated for any remaining aircraft at.Adding at least one additional aircraft to the formation (e.g., a firstformation) at the selected positions may include adding one additionalaircraft to the formation (e.g., the first formation) at the selectedposition, or adding another formation (e.g., a second formation) to theformation (e.g., the first formation) at the selected position. Thelatter scenario may include cases when a leader in the second formationbecomes a follower in the first formation and vice versa.

In accordance with embodiments of the present invention, a method ofadding an additional aircraft to an existing aircraft formation (similarto method 1900 in FIG. 19) is provided in which the following may beimplemented by the additional aircraft, either manually, automaticallyor both: establishing an initial handshake between aircraft in theexisting formation and the additional aircraft, coarse aligning theposition of the additional aircraft, vortex searching and tracking bythe additional aircraft, and fine aligning of the additional aircraftwith respect to other aircraft. Additional processes may include one ormore of establishing communication channel(s) and data exchangenetwork(s) between the aircraft, choosing formation flight metric andevaluating its parameters, optimizing relative aircraft positions tomaximize formation flight benefits by maximizing the metric parameters,and the like.

In accordance with embodiments of the present invention, a method 2100of preliminary and initial handshaking between at least two aircraft(shown in FIG. 21) is provided in which the following may be implementedby the two aircraft, either manually, automatically or both: sending andreceiving transponder signals by each aircraft at 2110, establishingtwo-way communication links between aircraft at 2120, and exchangingtelemetry data at 2130. The telemetry data may include information aboutsuch flight parameters as the position, airspeed, pitch angle, yawangle, thrust, power consumption and acceleration of an aircraft, statusand/or operating performance (e.g. power consumption) of on-boardsubsystems, such as propulsion systems, power systems, flight controlsystems, payload systems and other systems, data from various on-boardsensors including airflow data near the aircraft and so on. Additionalprocesses may include one or more of designating the roles of leadersand followers to specific aircraft at 2140, selecting the pattern, shapeand size for a formation at 2150, configuring flight control systems fora formation flight at 2160, and configuring payload for formation flighton at least one aircraft at 2170. The same aircraft in a formation mayundergo multiple handshaking steps. For example, it is possible for thesame aircraft to be both a leader and a follower, in which case thisaircraft may first go through the handshaking as a follower andsubsequently as a leader aircraft do different handshaking with otheraircraft (e.g., additional aircraft joining the formation).

In accordance with embodiments of the present invention, a method ofnetworking between at least two aircraft is provided in which thefollowing may be implemented by the two aircraft, either manually,automatically or both: establishing a communication network among theaircraft, exchanging telemetry data, and exchanging flight plans andcommands. Additional processes may include one or more of selectingnetworking channel(s) and protocol(s), establishing a peer-to-peernetwork, establishing an ad-hoc network, establishing a network usingradio frequency (RF) communication channels, establishing a networkusing free space optics, selecting and maintaining optimum distancesbetween aircraft for reliable communication links, extending a networkto elements outside of a formation (including other aircraft,ground-based network nodes (e.g., ground stations) and space-basednetwork nodes (e.g., communication satellites)), and the like. Theformation networking may be based on either mesh or point-to-pointcommunication links. Different aircraft may play either different orsimilar roles in the network. In the former case, at least one aircraftmay be a designated network controller, while in the latter case allaircraft equally share the tasks of managing network traffic.

In accordance with embodiments of the present invention, a method 2200of coarse alignment between two aircraft for a close formation flight(shown in FIG. 22) is provided in which the following may be implementedby the two aircraft, either manually, automatically or both: acquiringthe current relative positions of the aircraft at 2210, selecting targetpositions in the formation for each aircraft and their boundaries at2220, and adjusting coarse positions of each aircraft until they arewithin the target boundaries at 2230. The target position may correspondto approximate expected or estimated position of a wingtip vortex behinda leader aircraft. Additional processes may include one or more ofexchanging telemetry data between the aircraft, utilizing direct linksbetween the aircraft (e.g., network links), utilizing indirect linksbetween aircraft (e.g., via ground stations and satellites), usingvisual acquisition, recognition and analysis to obtain relativepositioning data (e.g., using video cameras or thermal imaging), usingbeacon signals to facilitate coarse alignment, using triangulation toanalyze data and calculate relative positions, and the like.

In accordance with embodiments of the present invention, a method 2300of fine aligning between two aircraft for a close formation flight(shown in FIG. 23) is provided in which the following may be implementedby the follower aircraft, either manually, automatically or both: vortexsensing at 2310, evaluating the displacement of a vortex core withrespect to the optimal position at 2320, and changing the aircraftposition at 2330. The method 2300 may be repeated until the desireddisplacement is achieved (e.g., zero displacement or displacement withina predetermined tolerance of zero). Additional processes may include oneor more of vortex searching, vortex tracking, evaluating the optimumposition of the vortex core with respect to the aircraft, choosing aformation metric, evaluating and optimizing the metric, and the like.Changing the aircraft position at 2330 may include changing thetransverse, streamwise or X position, changing the lateral, spanwise orY position, and changing the vertical or Z position of the followeraircraft with respect to the vortex core. Furthermore, a leader aircraftmay facilitate the process of fine alignment between the leader and thefollower by marking the approximate positions of its vortices, which inturn may be achieved by mechanical means (e.g., producing visual aidssuch as small particulates behind wingtips), electrical means (e.g., byionizing air and emitting ionized gas at the wingtips), optical means(e.g., by emitting optical beams along the streamwise direction behindthe wingtips), radio means (e.g. by emitting directional radio waves)and audio means (e.g., by emitting concentrated sound (or infra/ultrasound) waves along the streamwise direction behind the wingtips).

In accordance with embodiments of the present invention, a method ofchanging a formation flight pattern with at least one leader and onefollower aircraft is provided in which the following may implemented byat least two aircraft: reassigning the roles of one former leader tobecome a follower and one former follower to become a leader, updatingtarget positions for the respective aircraft, initiate position changein the formation by changing to coarse positions by the respectiveaircraft and perform fine aligning of the respective positions of eachaircraft in the formation.

In accordance with embodiments of the present invention, a method ofmetric evaluation of a close formation is provided in which thefollowing may be implemented by at least one follower aircraft, eithermanually, automatically or both: selecting an appropriate metric forevaluation of the flight formation (such as lift, drag, thrust, powerconsumption, fuel consumption, electrical consumption, electrical powersupply current and voltage, angle of attack, rate of descent or ascent,air speed, rolling moment, yaw moment, pitching moment, vortex coredisplacement and others), collecting data for evaluating the metric, andcalculating the metric using collected data. These processes may be usedrepeatedly and continuously during the formation flight to evaluate theconditions of a single pair formation (e.g., alignment between a leaderand a follower) or of a larger formation with multiple leader-followerpairs. Additional processes may include one or more of measuring airflowcharacteristics around the follower aircraft, exchanging data (measuredand calculated) between the aircraft, receiving additional data fromother aircraft, analyzing collected data, using averaging and filteringfor analyzing the data, using Kalman filters for data analysis andmetric calculations, providing data used in calculations to otheraircraft, providing the calculated metric to other aircraft in theformation, using several different metric parameters, switching betweendifferent metric parameters used for evaluation of the flight formation,and the like. Furthermore, in a formation with multiple followers acombined metric may be used to evaluate the formation as a whole, inwhich metric parameters from different followers are collected andanalyzed, and a single figure of merit is produced to characterize thestatus of the formation as a whole. The combined formation flight metricmay be the total propulsion power of an aircraft fleet in the formation,the total aerodynamic drag, the net fuel consumption of the fleet as awhole, the sum of quadrature deviations from the optimum relative vortexpositions in the formation and others.

In accordance with embodiments of the present invention, a method 2400of close formation optimization (shown in FIG. 24) is provided in whichthe following may be implemented by at least one follower aircraft,either manually, automatically or both: providing the results of themetric evaluation at 2410, changing flight parameters at 2420,evaluating changes in the metric at 2430, and providing feedback toflight control at 2440, for example, to continue to change the flightparameters if the metric changes are positive and reversing the changeif the metric changes are negative. The flight parameters that may bechanged during the formation optimization include, but are not limitedto: position, airspeed, pitch angle, roll angle, yaw angle,acceleration, thrust, power consumption, payload power consumption, andothers. For example, the aircraft altitude may be continuously varied ina search of a minimum power consumption position in the verticaldirection. Several flight parameters may be varied at the same time orsequentially. Additional processes may include one or more of providingflight parameter changes to other aircraft in the formation,coordinating flight parameter changes with actions of other aircraft(e.g., synchronizing or conversely alternating flight parameter scansbetween different aircraft), evaluating calculation errors andterminating the optimization process when effected changes are smallerthan the calculated errors, and the like. For example, two followeraircraft in a formation may vary their positions synchronously withoutaffecting each other evaluation of a formation flight metriccorresponding to their respective leader-follower pairs. As a result,the combined formation flight metric may be evaluated and optimizedfaster than if they were varying their positions in sequence.

The method 2400 may also include using a deep learning computeralgorithm for data processing and analysis during the formation flightoptimization, which may recognize and record optimum follower aircraftpositions with respect to either leader positions or vortex corepositions in different flight conditions (i.e., flight speeds,altitudes, crosswinds, aircraft size, formation configuration, etc.).Once this position is learned, it can be quickly replicated withprecision by the automatic flight control system after a particularvortex pattern is identified by the deep learning algorithm. As aresult, the formation flight optimization can be dramatically faster.

In accordance with embodiments of the present invention, a method ofmaintaining a close formation is provided in which the following may beimplemented by at least one follower aircraft, either manually,automatically or both: tracking a vortex produced by a leader aircraft,and adjusting the aircraft position with respect to the vortex coreuntil the optimum vortex position is achieved. The optimum position maybe defined in a number of ways, including but not limited to: a positionof an aircraft relative to a vortex center or a leader aircraft thatmaximizes a given formation metric (e.g., maximizes the aerodynamic dragreduction), a position at which at which formation flight control inputsare zero (e.g., vortex eye sensor measurements are zero or close to zeroas described below), a position predicted by a computer vortex model asbeing optimal for a given formation flight and so on. Of course, theoptimum position can be reliably maintained only within the measurementuncertainties and accuracy of on-board sensors, and capabilities andprecision of flight control systems. These processes may be repeatedcontinuously or intermittently by one or more aircraft in the formation.Changes in the relative position of vortices may be induced by themotion of leader aircraft and atmospheric air movements. Continuousvortex tracking allows follower aircraft to maintain a persistent lockon the vortex position, to implement timely adjustments in the aircraftposition and thus maintain an efficient close formation.

In accordance with embodiments of the present invention, another methodof maintaining a close formation is provided in which the following maybe implemented by both a leader and a follower aircraft, eithermanually, automatically or both: tracking the leader aircraft wingtipvortex by the follower aircraft, transmitting data containing relativeposition of the vortex by the follower aircraft to the leader aircraft,and adjusting the leader aircraft position with respect to the followeraircraft until the optimum vortex position is achieved. The datatransmission between the follower and the leader aircraft may be donevia a formation network or a dedicated communication link between thetwo aircraft.

In accordance with embodiments of the present invention, a method ofrecovering a close formation is provided in which the following may beimplemented by either a leader or a follower aircraft, either manually,automatically or both: alerting other aircraft in the formation of abroken formation between at least one leader and one follower,initiating vortex recovery by the follower aircraft, and maintainingclose formation between other aircraft in the formation. The leaderaircraft may also assist in the vortex recovery by one or more ofcomplimentary adjustments in its relative position to the followeraircraft and provision of additional positioning telemetry data to thefollower aircraft. The positioning tolerances and relevant formationmetrics may be relaxed for other aircraft in the formation during theformation recovery period. The aircraft assignments in the formation donot change in the formation recovery, i.e., their relative positionsbefore and after recovery remain the same.

In accordance with embodiments of the present invention, a method ofchanging a close formation is provided in which the following may beimplemented by either a leader or a follower aircraft, either manually,automatically or both: disengaging a close formation alignment betweenat least one leader and a follower aircraft, reassigning aircraft to newpositions in the formation, and producing a new formation based on thenew position assignments. Disengaging a close formation alignmentbetween at least one leader and a follower aircraft may includeterminating vortex tracking by the follower aircraft and entering a newflight path for either the follower aircraft, the leader aircraft, orboth.

In accordance with embodiments of the present invention, the closeformation methods outlined above may be implemented by the flightcontrol systems internal and external to the aircraft and aircraftformation as a whole. FIG. 25 shows an exemplary fixed-wing aircraft2500 configurable for a close formation flight, which comprises afuselage 2510, a wing 2520, a tail 2530, and a propulsion system 2540.Other aircraft configurations may be used, in which additional elementsmay be present or some elements may be missing, but at least one wing ora wing-like surface is present. These configurations include but notlimited to, for example, planes with multiple wings (such as biplanes,canard wings, etc.), planes with multiple tails and or fuselages, planeswith additional sections (such as pods, booms, adaptive andshape-shifting elements and others), wing-shaped airships, verticaltake-off and landing (VTOL) aircraft, parasailing aircraft, wing-bodyaircraft (without a fuselage), tailless aircraft, aircraft withdifferent propulsion systems (single-engine, multi-engine,propeller-based, turbo-based, jets, etc.), and so on.

In accordance with embodiments of the present invention, the aircraft2500 may be equipped with a flight control system 2550, airflow sensors2560 and 2561, flight control surfaces 2570, 2571 and 2572, andelectrical wiring between these elements (e.g., 2580 and 2581). Theflight control system 2550 may be fully autonomous, as for example onboard of a UAV. On a manned aircraft, the flight control system 2550 maybe manual, semi-autonomous, or fully autonomous. Typically, a mannedaircraft has at least some autonomous flight control functionality,i.e., auto-pilot capabilities. The flight control system 2550 maymonitor flight data provided by the sensors 2560 and 2561, analyze them,and provide necessary control inputs to the flight control surfaces2570, 2571 and 2572 (or other flight control elements on the aircraft)and propulsion system 2540 in order change any of the flight parameters,including airspeed, roll, yaw and pitch angles, acceleration, rate ofdescent/ascent, turning rate, etc.

In accordance with embodiments of the present invention, FIG. 26 showsthe flight control architecture 2600 for a group of aircraft 2620 inclose formation fleet 2610. Flight control systems 2625 on each aircraft2620 in cooperation with each other establish the overall control of theformation fleet 2610. This cooperation may be enabled in part by thevortex sensing capabilities and in part by the communication andnetworking capabilities on at least some aircraft within the formation2610. In addition, individual flight control systems 2625 on eachaircraft 2620 may have dedicated software and hardware modules, whichare tasked exclusively with functions of maintaining and controlling aclose formation flight. The aircraft 2620 may be identical to each otheror different. The flight control capabilities of the formation as awhole may be enhanced by other communications, including communicationswith other aircraft 2630 outside of the formation 2610, ground flightcontrol stations 2640, and satellites 2650. These communications mayhelp to establish, maintain and modify the formation 2610. Otheraircraft 2630 may include for example aircraft that aims to join theformation 2610 or that have left the formation 2610. Ground flightcontrol station 2640 may provide navigation services, flight plans, andother general flight commands to the formation 2610 via directcommunication links. Satellites 2650 may provide similar services aswell as indirect communication links with the ground flight controlstations when direct communication links are not available.

Flight control tasks may be shared in the formation 2610 by individualflight controllers (i.e., flight control system 2625). These tasks maybe performed by the respective onboard flight controllers oralternatively processors dedicated to flight formation tasks primarily,including data analysis, follower aircraft guidance, networking andcommunications inside the formation. A peer-to-peer network may beformed by the flight control systems 2625 to share flight control tasksequally. Alternatively, some flight control tasks may be delegated tothe flight control systems on specific aircraft. For example, there maybe at least one aircraft in a formation that is assigned the leaderrole. Such an aircraft (or several of them) may perform the navigationaltasks for the whole fleet, including negotiating, setting, modifying andadjusting flight plans and waypoints. Flight control systems on otheraircraft in this case may serve the functions of maintaining closeformation exclusively.

Some formation flight tasks may be distributed across all or severalaircraft. For example, evaluation of the combined flight formationmetric may be shared so that each aircraft contributes its share in itscalculation. Also, a formation flight health status may be evaluation inthe same way by all formation aircraft, which may including flightstatuses from all aircraft. In cases when one or more aircraft statusreaches alarm level (e.g. relatively high battery depletion or higherfuel consumption with respect to other aircraft), this condition maytrigger a change in the formation flight configuration, where one ormore aircraft may move into a more favorable position (e.g., a leadermay move into a follower position). A predetermined critical level of anindividual aircraft flight status may be set for example at 5-10% higherbattery depletion state relative to other aircraft. Alternatively,aircraft may be rotated on a periodic basis to ensure even batterydepletion across the formation fleet.

To enable effective close formation flight control, several vortexsensing approaches may be implemented. In accordance with embodiments ofthe present invention, FIG. 27 shows an aircraft 2700 equipped with aseries of airflow sensors: sensors 2715 mounted on a fuselage 2710,sensors 2725 mounted on a wing 2720 and sensors 2735 mounted on a tail2730. The function of these sensors is provide the flight controllerwith data characterizing the three-dimensional airflow around theaircraft (i.e., airflow along the three X, Y, and Z directions/axes).This data may then serve as the basis to extract sufficient informationabout the vortices near the aircraft 2700. The airflow sensors may bepositioned on the body of the aircraft so that the air flow is notperturbed by the aircraft at the point of sensing, for example usingstand-off booms, beams, long rods, bars, etc. In addition, other datamay be used in combination with the airflow sensor data to facilitatethe airflow analysis, including GPS positioning data (spatial position,orientation and acceleration), inertial navigation system data,telemetry data, data from other aircraft, data from ground controlsystems, data from weather control stations, data from air trafficcontrol and so on.

Furthermore, FIG. 28 shows an aircraft 2800 that may be equipped with atleast two types of airflow sensors: sensors 2825 and 2826. Differentsensors may perform different types of sensing, e.g., measurements ofairflow speed, airflow direction, air pressure, air temperature, angleof attack, and so on. Also, they may be positioned differently, i.e., ondifferent parts or different location of the airframe as shown in FIG.28. The methods for close formation flight outlined above andparticularly the method of vortex sensing may use airflow sensors shownin FIGS. 27 and 28 to collect data for constructing the computer vortexmodel. Aircraft 2700 and 2800 both use arrayed sensors or sensor arrays,as represented by the sensors 2715, 2725, 2735, 2825 and 2826,respectively, to characterize the airflow around each aircraft, providerelevant measurements and deliver data to a flight control system foranalysis, creation and update of a vortex model.

In addition, the aircraft as a whole may be used as an airflow sensor.For example, an upwash created by a vortex may induce a rolling momentin an aircraft. This situation is illustrated in FIG. 29, where a dualclose formation 2900 is shown consisting of two aircraft: a leaderaircraft 2910 and a follower aircraft 2930. The leader aircraft 2910produces a wingtip vortex 2920 on its left-hand side, which in turnproduces excess lift on the right half of the wing of the followeraircraft 2930, while the lift of the left half of the wing remainsnearly the same as that outside the formation. As a result, the followeraircraft 2930 is subjected to a counter-clockwise rolling moment 2940.In order to compensate for this moment and remain level, a flightcontrol system may use flight control surfaces (such as ailerons) tointroduce a counter-rolling moment in the opposite direction. The flightcontrol signal required to maintain the follower aircraft in the levelposition (e.g., the magnitude of aileron's deflection) may serve as ameasure of the vortex 2920 relative position with respect to thefollower aircraft 2930. The optimum vortex position may be near theposition at which this moment is maximized. Therefore, various peaksearching algorithms may be implemented to maximize the rolling momentand as a result bring the relative positions between the two aircraftclose to the optimum position. This method may be used for vortexsearching, vortex sensing, vortex tracking, coarse alignment and finealignment described above.

In accordance with embodiments of the present invention, airflow sensorsand probes for characterization of air flow around an aircraft may bepositioned in special key locations on the aircraft that can simplify,accelerate or otherwise enhance the process of vortex searching, sensingand tracking. FIG. 30 shows an airflow sensing system 3000, in which anaircraft 3010 has airflow sensors 3015 and 3016 mounted at two speciallocations of the wing 3020. These locations correspond to the optimumpositions of a vortex center (or the center of a vortex core) 3030 onboth sides of the wing. The optimum vortex position is defined as theposition at which there is a maximum formation benefit to the followeraircraft, e.g., maximum drag reduction. These positions can becalculated and sensors can be designed and mounted in these positionsfor a given vortex distribution before the formation flight. In general,the optimum vortex position depends weakly on the vortexcharacteristics, e.g., its size, core radius, etc. Therefore, thesesensor positions can be located with high accuracy at the design andproduction phases in aircraft manufacturing.

Airflow sensors 3015 and 3016 may provide airflow data, suchinstantaneous air velocities and their vectors at their locations,including their projections on coordinate axes: V_(X), V_(Y), and V_(Z).When the vortex 3030 is centered on the sensor 3015 (or alternatively3016), V_(Y) and V_(Z) magnitudes should be close to zero. Accordingly,since sensors 3015 and 3016 determine to the location of the vortex“eye” (i.e., its core), they may be termed as vortex eye sensors or eyesensors. When a vortex is displaced, V_(Y) and V_(Z) magnitudes providedby eye sensors become positive or negative depending on the direction ofthe displacement. This is illustrated in FIG. 31, which shows a graph3100 of the vertical air velocity V_(Z) produced by an eye sensor versusthe lateral (spanwise) displacement of the vortex Y with respect to theeye sensor. For negative displacements in this case, where the aircraft3110 shifts left with respect to the vortex 3115, V_(Z) becomespositive. Conversely, for positive displacements in this case, where theaircraft 3120 shifts left with respect to the vortex 3125, V_(Z) becomesnegative. Therefore, the sign and the magnitude of the V_(Z)measurements provided by the eye sensor may be used directly by theflight control system for course correction and vortex tracking withoutcomplicated data analysis, which simplifies flight control and makes itmuch faster and responsive. Similar results may be achieved with V_(Y)measurements provided by an eye sensor, which in turn may be used tocontrol the Z position with respect to the vortex core.

In accordance with embodiments of the present invention, severalspecialized airflow sensors may be used for vortex sensing describedabove. They include airflow sensors and probes based on Pitot tubes,vanes, hot wires and others of different designs as described below.

A cross-section of a Pitot tube 3200 used for air speed measurements isshown in FIG. 32, in which there are two air channels 3210 and 3220. Theair channel 3210 may be used to measure the dynamic pressure, which isinfluenced by the air speed, while the air channel 3220 may be used tomeasure the static pressure, which is not influenced by the air speed.The difference between the dynamic and static pressures may then be usedas a measure of the air speed. This device is not capable of measuringthe complete air velocity vector, including V_(Y) and V_(Z) components.

In accordance with embodiments of the present invention, a specializedairflow probe 3300 based on a Pitot tube approach as shown in FIG. 33may be used to measure V_(Y) and V_(Z) components. The airflow probe3300 includes two air channels 3310 and 3320 with input port facing inopposite directions from each other and perpendicular to the streamwisedirection 3330. The input ports may be aligned either in the verticaldirection (as shown in FIG. 33) or in the horizontal direction (or inany other plane if required), which is indicated as the probemeasurement axis 3340. In the absence of the air flow in the directionof the probe's measurement axis 3340, the air pressure in the twochannels 3310 and 3320 is the same and the difference between their airpressures is zero. In the presence of the air flow in the direction ofthe probe's measurement axis 3340 (e.g., non-zero V_(Z) when themeasurement axis is the Z-axis), the difference between the airpressures in the two channels 3310 and 3320 is proportional to thesquare of the air velocity in this direction (e.g., V_(Z)).

In accordance with embodiments of the present invention, a specializedairflow probe 3400 based on a Pitot tube approach as shown in FIG. 34may be used to measure V_(Y) and V_(Z) components. The airflow probe3400 includes two air channels 3410 and 3420 with input port facing indirections at the right angle from each other (or other angle greaterthan 0 and less than 180 degrees). The input port of channels 3410 and3420 may also be positioned symmetrically with respect to the streamwisedirection of the probe 3430. The input ports may be aligned either inthe vertical direction (as shown in FIG. 34) or in the horizontaldirection (or in any other plane if required), which is indicated as theprobe measurement axis 3440. In the absence of the air flow in thedirection of the probe's measurement axis 3440, the air pressure in thetwo channels 3410 and 3420 is the same and the difference between theirair pressures is zero. In the presence of the air flow in the directionof the probe's measurement axis 3440 (e.g., non-zero V_(Z) when themeasurement axis is the Z-axis), the difference between the airpressures in the two channels 3410 and 3420 is proportional to the airvelocity in this direction (e.g., V_(Z)).

In the description below probes of the type shown in FIGS. 33 and 34 aredefined as differential airflow probes. In accordance with embodimentsof the present invention, a specialized airflow sensor 3500 based on thedifferential airflow tube design may be used to measure air flow speedand direction as shown in FIG. 35. The airflow sensor 3500 includes anairflow probe 3510, comprising at least two air channels 3520 and 3525,air connectors 3530 and 3535, and a transducer 3540. The airflow probe3510 may be one of the probes 3300 and 3400, or similar. In general, theairflow probes may have different forms and shapes and be characterizedby the same basic designs shown in FIGS. 33 and 34. The air connectors3530 and 3535 (e.g., air pressure tubes) may be used to provide airpressure inputs for the transducer 3540, which provides and electricaloutput signal 3550 proportional to the difference between the airpressures in the channels 3520 and 3525.

The airflow sensor 3500 may also comprise additional airflow probes andtransducers connected to these probes. The airflow probes may beintegrated into one or more units. Similarly the transducers may beintegrated into one or more units. The transducers may also beintegrated in one unit with the probes to minimize air pressuredistortions from the connectors. Different airflow probes may havedifferent measurement axes, so that air flow velocity vectors may bemeasured in all directions and full characterization of air flow may beprovided as a result.

In accordance with embodiments of the present invention, a specializedairflow probe head 3600 may be used for air flow measurements as shownin FIG. 36. The probe head 3600 may include a cone-shaped top 3610 andair channels 3620 and 3625 separated by a wall 3630. A cone-shaped topmay be used to minimize air resistance and disturbance in the air flowby the probe itself. Large openings for air channels 3620 and 3625improve probe sensitivity to small air flows (low air speeds) in themeasurement axis direction. The probe measurement axis may beperpendicular to the streamwise direction of the probe (e.g., verticalin FIG. 36).

Another specialized airflow probe head 3700 may be used for air flowmeasurements as shown in FIG. 37. The probe head 3700 may also include acone-shaped top 3710 and air channels 3720 and 3725 separated by a wall3730. In addition, the probe head 3700 may include fins 3740 and 3745for streamlining air flow through the air channels 3720 and 3725. Thefins may be aligned parallel to the probe measurement axis or side wallof the air channels. Both probe head designs and other similar probehead designs may be implemented in the airflow probes and sensorsdescribed above (e.g., 3300, 3400, and 3500).

In accordance with embodiments of the present invention, a specializedairflow probe head 3800 may be used for air flow measurements as shownin FIG. 38. The probe head 3800 may include an oblong top 3810 and airchannels 3820 and 3825 separated by a wall 3830. The air channels may beangled with respect to the measurement axis and the streamwise direction(e.g., they may form 45 degree angle with the vertical measurement axisand the streamwise direction in FIG. 38). Although a 45 degree angle isshown in FIG. 38, other angles may also be used as described above withrespect to FIG. 34. In addition, the probe head 3800 may include fins3840 and 3845 for streamlining air flow through the air channels 3820and 3825, respectively. The fins may be aligned parallel to the sidewall of the air channels and form the same angles with respect to themeasurement axis and the streamwise direction as the channels as awhole.

Another specialized airflow probe head 3900 may be used for air flowmeasurements as shown in FIG. 39. The probe head 3900 may also includean oblong top 3910 and pluralities of air channels 3920 and 3925separated by a walls 3930, 3940 and 3945. The group of air channels 3920is connected to the common channel 3950, and the group of air channels3925 is connected to the common channel 3955. Both probe head designs3800 and 3900 and other similar probe head designs may be implemented inthe airflow probes and sensors described above (e.g., 3300, 3400, and3500).

In accordance with embodiments of the present invention, FIG. 40 shows athree-dimensional view of a specialized airflow probe head 4000,comprising an aerodynamically efficient oblong body 4010 and at leastone pair of air channels 4020 (the opposite side air channel opening isnot visible in FIG. 40). Similarly, FIG. 41 shows a three-dimensionalview of a specialized airflow probe head 4100, comprising anaerodynamically efficient oblong body 4110 and plurality of parallel airchannels 4120 (the opposite side air channel openings are not visible inFIG. 41). A larger number of parallel air channels may lead to anincreased sensitivity to small airflows and small variations in theairflow in the direction of the measurement axis.

FIG. 42 shows a three-dimensional view of a specialized airflow probehead 4200, comprising an aerodynamically efficient oblong body 4210 andplurality of parallel air tubes 4220 and 4225. The air tubes 4220 and4225 may be used as extended openings for inner air channels (e.g., airchannels 4120 in FIG. 41). The channel extension may allow more accuratemeasurement of air flow velocity vectors and their variations by movingthe channel openings away from the probe body 4210.

In accordance with embodiments of the present invention, FIG. 43 showscross-sections of airflow probe heads 4310 and 4320 in the planeperpendicular to the probe streamwise direction (e.g., X axis). Theprobe head 4310 may have at least one pair of measurement air channels4311 and 4312, which in this case may provide measurements of airvelocity in the vertical direction (i.e., V_(Z)). When rotated, the sameprobe head 4310 may provide measurements of air velocity in thehorizontal direction (i.e., V_(Y)). The probe head 4320 may have atleast two pairs of measurement air channels: 4321 and 4322, and 4323 and4324, which may provide simultaneous measurements of air velocity inboth vertical and horizontal directions (i.e., V_(Y) and V_(Z)).Additional air channels may also be provided: for example, a standardPitot channel may be provided for the measurements of a streamwise airspeed component (i.e., V_(X)), so that a complete air velocity vectormay be obtained.

In accordance with embodiments of the present invention, FIG. 44 showsan airflow probe 4400 comprising an array of airflow probe heads 4410,similar to the airflow probe head 4100. Each airflow probe head 4410 mayhave output ports 4420 and 4421, which in turn may be connected to thecommon ports 4430 and 4431. The common ports may then be connected to acommon air pressure transducer for differential pressure measurements.This approach allows one to collect and average several probe airpressure measurements, thus improving signal resolution and measurementsensitivity.

In accordance with embodiments of the present invention, FIG. 45 shows athree-dimensional view of an airflow probe 4500, the body 4510 of whichis a thin plate. The airflow probe 4500 has two pairs of air channelswith multiple openings on wider sides of the body; the top openings 4520are visible in FIG. 45. The air channels have output ports 4530 and4531, which may be used for connection to the air pressure transducer.The probe measurement axis may be perpendicular to the wider side of theprobe body 4510 (i.e., vertical in FIG. 45). The shape of the body 4510may be rounded to decrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 46 shows athree-dimensional view of an airflow probe 4600, the body 4610 of whichis a thin plate. The airflow probe 4600 has two pairs of air channelswith multiple openings on wider sides of the body; the top openings 4620are visible in FIG. 46. The air channels have output ports 4630 and4631, which may be used for connection to an air pressure transducer.The probe measurement axis may be perpendicular to the wider side of theprobe body 4610 (i.e., vertical in FIG. 46). The shape of the body 4610may be rounded to decrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 47 shows athree-dimensional view of an airflow probe 4700, the body 4710 of whichis a thin plate. The airflow probe 4700 has two pairs of air channelswith multiple openings on narrower sides of the body; the side openings4720 are visible in FIG. 47. The air channels have output ports 4730 and4731, which may be used for connection to an air pressure transducer.The probe measurement axis may be perpendicular to the narrower side ofthe probe body 4710 (i.e., horizontal in FIG. 47). Measurements in thisdirection may be less affected by the shape of the body than in theorthogonal direction. The shape of the body 4710 may be rounded todecrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 48 shows athree-dimensional view of an airflow probe 4800, the body of which is athin plate. The airflow probe 4800 has a pair of air channels withsingle openings on narrower sides of the body. The air channels have twooutput ports, which may be used for connection to an air pressuretransducer. The probe measurement axis may be perpendicular to thenarrower side of the probe body (i.e., horizontal in FIG. 48).Measurements in this direction may be less affected by the shape of thebody than in the orthogonal direction. The shape of the body may berounded to decrease aerodynamic resistance.

In accordance with embodiments of the present invention, FIG. 49 showsairflow sensor array system 4900, in which a plurality of airflowsensors 4920 are mounted on a wing 4910. Each sensor comprises anairflow probe 4921 and at least one air pressure transducer 4922.Various numbers of airflow sensors may be used in the system 4900, thegreater number of sensors results in a finer (better) spatial resolutionin the airflow measurements and subsequent mapping of a vortex field.

Alternatively, an airflow sensor system 5000 shown in FIG. 50 may beused for airflow characterization and vortex sensing, which comprises apair of airflow sensors 5020 and 5030 mounted in specific locations atdistances 5040 from the center line of the wing 5010. The specificlocations correspond to the optimum positions of vortex centers withrespect to the wing 5010. Furthermore, the left-hand side airflow sensor5020 may comprise air pressure probes 5021 and 5022, which may haveorthogonal to each other measurement axes (e.g., Y and Z axis) andconnected to the air pressure transducers 5023 and 5024, respectively.The right-hand side airflow sensor 5030 may comprise air pressure probes5031 and 5032, which may have orthogonal to each other measurement axes(e.g., Y and Z axis) and connected to the air pressure transducers 5033and 5034, respectively. The airflow sensor system 5000 is an eye sensor,which enables a flight control system to effectively and quickly trackvortices on both sides of the aircraft. The sensors 5020 and 5030 may beused together or separately. For example, while one sensor (e.g., sensor5020) is used to track a vortex, the other sensor (5030) may be used asa reference to subtract any airflows caused by the aircraft motion.Alternatively, additional reference sensors may be mounted on a wing orother parts of the aircraft.

In accordance with embodiments of the present invention, FIG. 51 showsan alternative airflow probe 5100. The airflow probe 5100 may include anoblong body 5110, at least one vane 5120 and at least one vane 5130 inorthogonal direction. During the airflow measurements, the vanes mayalign themselves along the direction of the airflow. The deflectionangle for each vane may be measured to represent the air velocity anglewith respect to a particular axis or direction, primarily the streamwisedirection (e.g., the X axis). These measurements of the air velocityvector angles with respect to the streamwise direction of the probe 5100can be combined with the air speed measurements from a standard Pitottube sensor to obtain a complete air velocity vector. For example, thevane 5120 may provide measurements of the spanwise component of airvelocity V_(Y), the vane 5130 may provide measurements of the verticalcomponent of air velocity V_(Z).

In accordance with embodiments of the present invention, FIG. 52 showsanother vane-based airflow probe 5200. The airflow probe 5200 mayinclude an oblong body 5210, a first array of vanes 5220 and a secondarray of vanes 5230 in the orthogonal direction. During the airflowmeasurements, the vanes may align themselves along the direction of theairflow. The deflection angle for each vane may be measured to representthe air velocity angle with respect to a particular axis or direction,primarily the streamwise direction (e.g., the X axis). Similar to theprobe 5100, the vane array 5220 may provide measurements of the spanwisecomponent of air velocity V_(Y), the vane array 5230 may providemeasurements of the vertical component of air velocity V_(Z). The vanearray may improve the accuracy of measurements in comparison to that ofa single vane.

FIG. 53 further illustrates the working principle of the vane airflowprobe by showing a cross-section of a vane airflow probe 5300, whichcomprises a body 5310, a first set of vanes 5320 and a second set ofvanes 5330. The vanes may rotate under the influence of the airflowaround the body 5310 as shown in FIG. 53. The rotation angle mayregistered and measured by a transducer attached to each vane. The vanesand vane arrays may be also mounted on stand-off mounts to eliminatepotential interference with the probe body.

In accordance with embodiments of the present invention, FIG. 54 showsalternative airflow probe 5400 based on a hot wire principle. The probe5400 includes at least one hot wire 5410 and an optional second hot wire5420 connected to electrical prongs 5430. Electrical current may be usedto heat the hot wires 5410 and 5420. Airflow perpendicular to a hot wiremay cool the wire, changing its temperature. The temperature change thencan be used as the measure of the air velocity normal to the wire.Alternatively, the hot wire current may be adjusted to keep thetemperature constant, in which case the current change may serve as themeasure of the air velocity.

In accordance with embodiments of the present invention, FIG. 55 showsan alternative airflow sensor 5500 based on a hot wire principle. Thehot wire sensor 5500 comprises a hot wire probe 5510, mounts 5520, asensor holder 5530, and the electrical circuit 5540 used to monitor theresistance of the hot wire probe 5510. The hot wire may be made fromtungsten or platinum, so that small changes in hot wire temperature mayproduce noticeable changes in its electrical resistance. As a result,air velocity may be directly measured by the electrical circuit 5540.Multiple hot wire probes may be combined to produce multiplemeasurements of air velocity in different directions and thus fullycharacterize the air velocity vector.

In accordance with embodiments of the present invention, FIG. 56 showsanother alternative airflow sensor 5600 based on a hot film principle.The hot film sensor 5600 comprises a hot film probe 5610, electricalcontacts 5620, a sensor housing 5630, and the electrical circuit 5640used to monitor the resistance of the hot film probe 5610. The hot filmprobe operates similarly to the hot wire sensor, i.e., it changes itstemperature in response to the air flow across its surface. Thetemperature changes induce either changes in resistance or electricalcurrent, which may be measured directly by the electrical circuit 5640.

Multiple hot film probes may be combined to produce multiplemeasurements of air velocity in different directions and thus fullycharacterize the air velocity vector. FIG. 57 shows cross-sections oftwo orthogonal hot film probes 5710 and 5720, in which hot films 5715and 5725 respectively may be deposited on the inside of round openingsin the body or housing of the probe. As a result, air velocitycomponents in orthogonal directions (e.g., V_(Y) and V_(Z)) may beeffectively measured and used in characterization of a wingtip vortex.

In accordance with embodiments of the present invention, differentapparatus and methods may be used to assist the vortex searching andcoarse aligning with a vortex in a close formation. Although describedseparately, the following apparatus and methods to assist the vortexsearching and coarse aligning with a vortex may be used in anycombination with each other. For example, FIG. 58 shows free-spaceoptics system 5800, in which a leader aircraft 5810 is equipped with anoptical source (e.g., a laser or a high power light emitting diode) toproduce a light beam 5830 at one of the wingtips along the streamwisedirection towards a follower aircraft 5820. The follower aircraft 5820is equipped with a light detector 5825 (or light sensor array), whichcan be used to detect and monitor the light beam 5830. The light beam5830 may approximately follow the path of a wingtip vortex andfacilitate the vortex search.

Instead of the light detector 5825, the follower aircraft 5820 may beequipped with a video camera and a thermal imaging device. A video orimaging camera may provide imaging data that may be used for imaginganalysis and achieve the same functionality as that of system 5800 evenwithout the light source 5815. However, this may require additionalcomputer processing capabilities on board of the follower aircraft.

Alternatively, the system 5800 may be substituted with sound producingand receiving apparatus to achieve the same functionality. For example,the light source 5815 may be replaced with a directional sound emitterto produce a sound cone (e.g., using ultrasound frequencies), while thelight detector 5825 may be replaced with a sound receiver. Changes insound intensity or frequency may then reflect changes in the relativepositions between the sound cone and the follower aircraft.

In accordance with embodiments of the present invention, FIG. 59 showsanother system 5900 that may facilitate vortex searching and coarsealigning for a close formation. In system 5900 a leader aircraft 5910may be equipped with a particle emitter 5915, which may be used toproduce a thin trail 5930 of small particles (e.g., smoke) behind itswingtips. The trail 5930 may be identified by onboard cameras 5925 of afollower aircraft 5920. The trail 5930 may better reflect the path ofwingtip vortices in comparison to light or sound beams.

In accordance with embodiments of the present invention, FIG. 60 showsanother system 6000 that may facilitate close formation flight. Insystem 6000 an aircraft 6010 and optionally an aircraft 6020 may eachcontain a plurality of radio antennas 6015 and 6025, respectively. Theseantennas may be operated as phase coherent arrays by onboard radioprocessing systems 6017 and 6027 respectively disposed on each aircraft6010 and 6020. An antenna array (antennas 6015 or 6025) may link aparticular aircraft to other aircraft, to ground-based network nodes(e.g., ground stations) or to space-based network nodes (e.g.,communication satellites). Alternatively, it may provide a dedicatedreference radio signal for relative position measurements by otheraircraft. Such a signal may be directional and concentrated in somedirections, for example in the plane of a flight formation. Spatialselectivity and channel propagation characteristics may be furtherimproved by receiving or transmitting with phase coherence acrossmultiple planes in the formation.

Changes in the relative phase delay between any two antennas from agiven array (e.g., array 6015 or array 6025) will then provideinformation about changes in the relative positions of the correspondingpoints on planes in the formation. For example, these measurements ofrelative phase delays may provide estimates of relative positionsbetween the planes (e.g., 6010 and 6020) along the Y and Z axes, as wellas their relative angular orientation including pitch, roll and yawangles. These phase delays may be measured by antennas that are usedprimarily for communications, or antennas dedicated for formation flightposition measurements, or antennas used for both purposes withindifferent frequency bands. If phase measurements are sufficientlyaccurate, they may also provide data about bending and other distortionsof wing surfaces useful for aerodynamic optimization of formation flightwith the help of Kalman filters, neural networks or deep learningalgorithms, or any of the many other measurement and control methodsdescribed above. These measurements may provide on-board flightcontrollers with additional flight data to assist in coarse and finealignment for the formation flight.

FIG. 61 shows a method 6100 of sensing three dimensional airflow by anaircraft in accordance with at least some embodiments of the presentinvention. The method 6100 includes collecting measurementscharacterizing airflow near the aircraft at 6102, analyzing thecollected measurements at 6104, creating, by a processor, a computermodel predicting one or more 3D airflow patterns parameter values basedon the analyzing at 6106, obtaining one or more additional measurementscharacterizing airflow near an aircraft of the plurality of aircraft at6108, and evaluating an error between an airflow parameter valuepredicted by the computer model and the one or more additionalmeasurement at 6110.

In some embodiments, measurements collected during the collecting at6102 include at least one of airflow velocity, airflow speed, airflowdirection, air pressure, air temperature, or an aircraft angle of attackof the aircraft. In the same or other embodiments, at least somemeasurements collected during the collecting at 6102 may be derived fromflight control signals applied to one or more control surfaces of theaircraft. In some embodiments, method 6100 includes varying at least oneflight parameter of the aircraft prior to obtaining at least onemeasurement of the one or more additional measurements. The at least oneflight parameter may include at least one of an aircraft angle ofattack, heading, altitude or velocity. The computer model created duringthe creating at 6106 may be a 3D model of a vortex field.

FIG. 62 shows a method 6200 of searching for an airflow pattern by anaircraft in accordance with at least some embodiments of the presentinvention. The method 6200 includes defining a target search arearelative to an aircraft at 6202, establishing a dithering flight patternintersecting with the target area at 6204, collecting, measurementscharacterizing airflow near the aircraft at 6206, analyzing thecollected measurements at 6208, and determining a location of an airflowpattern based on the analyzing at 6210. In some embodiments, at leastsome measurements collected during the collecting are derived fromflight control signals applied to one or more control surfaces of theaircraft. In some embodiments, the target search area is defined at 6202is defined with respect to a second aircraft.

In some embodiments, the determining at 6210 comprises performingcontinuous vortex sensing using a plurality of airflow sensorsdistributed along a spanwise direction of an aircraft wing andpositioned on stand-off booms in front of a leading edge of the aircraftwing. In some embodiments, the determining at 6210 comprises performingcontinuous vortex sensing using a plurality of airflow sensorsdistributed along a spanwise direction of an aircraft wing andpositioned on stand-off booms in front of a leading edge of the aircraftwing, and in some embodiments, the determining at 6210 comprisesperforming continuous vortex sensing using an airflow sensor on at leastone of a fuselage of the aircraft, a tail of the aircraft, a tail of theaircraft, and a nose of the aircraft.

In some embodiments, establishing the dithering pattern at 6204comprises varying at least one flight parameter of the aircraft relativeto a second aircraft during the collecting.

FIG. 63 shows a method 6300 of vortex tracking by an aircraft inaccordance with at least some embodiments of the present invention. Themethod 6300 includes receiving airflow data from an airflow sensor onthe aircraft at 6302, analyzing the airflow data by an onboard processorat 6304, mapping at least a part of the vortex field by the onboardprocessor at 6206, identifying the location of a vortex core at 6208,and measuring the position of the vortex core with respect to theaircraft at 6210. In some embodiments, method 6300 further includessubdividing the vortex field into different vortex regions andidentifying locations of respective vortex cores.

FIG. 64 shows a method 6400 of operating aircraft for flight in closeformation in accordance with at least some embodiments of the presentinvention. The method 6400 includes establishing a communication linkbetween a first aircraft and a second aircraft at 6402, assigning to atleast one of the first aircraft or the second aircraft, via thecommunication link at initial positions relative to one another in theclose formation at 6404, providing flight control input for aligning thefirst and second aircraft in their respective initial positions at 6406,tracking, by at least one aircraft in the close formation, at least onevortex generated by at least one other aircraft in the close formationat 6408, and based on the tracking, providing flight control input toadjust a relative position between the first aircraft and the secondaircraft at 6410. In some embodiments, method 6400 further includesdesignating the roles of leader and follower to one or both of the firstand second aircraft, selecting the formation pattern, shape and size fora formation, configuring flight control systems for a formation flight,and configuring payload for formation flight on at least one aircraft.

In some embodiments, the tracking at 6408 includes collecting airflowmeasurements, at the second aircraft, for sensing a first vortexgenerated by a wingtip of the first aircraft. The collected measurementsmay include at least one of airflow velocity vector, airflow speed,airflow direction, air pressure, air temperature, or an aircraft angleof attack of the second aircraft.

In some embodiments, the flight control input provided at 6406 includeschanging one of an aircraft heading, altitude, roll, pitch, yaw, thrustor velocity. In some embodiments, method 6400 includes at least one ofevaluating formation flight parameters and optimizing aircraft positionsto maximize formation flight benefits based on the evaluation and/orestablishing a data exchange network between the aircraft and exchangingtelemetry data.

In some embodiments, method 6400 further includes at least one ofproducing a model of a vortex field by an on-board processor, preservingthe model of the vortex field in a memory of the processor, initiating avortex search, reacquiring a vortex pattern, updating the vortex modeland/or providing continuous updates for vortex model characteristics onat least one aircraft. In some embodiment, method 6400 may furtherinclude navigating the formation as a whole to a destination position bythe first aircraft. The tracking may be provided by the second aircraftand may further include defining a first target search area relative tothe first aircraft, establishing, for the second aircraft, a ditheringflight pattern intersecting with the first target search area,collecting, at the second aircraft, measurements characterizing airflownear the second aircraft, and determining a location of a first vortexby analyzing measurements collected at the second aircraft.

In some embodiments, method 6400 may include determining a location of acore of the at least one vortex, evaluating a displacement between thecore of a first vortex and the second aircraft, changing a position ofat least one of the first aircraft or the second aircraft and repeatingthe determining and evaluating until a desired displacement is achieved.In an embodiment, at least one of a transverse position, lateralposition and vertical position of the second aircraft is changed withrespect to the core of a vortex or the cores of multiple vortices.

In some embodiments, method 6400 further includes marking an approximateposition of the at least one vortex. The marking may comprise emittingone or more of a stream of small particulates, ionized gas, radio waves,sound waves, and/or optical beams along a streamwise direction behindone or more wingtips of aircraft in the close formation.

FIG. 65 shows a method 6500 of operating aircraft in a close formationflight in accordance within one or more embodiments of the presentinvention. The method 6500 comprises determining relative positionsbetween a first aircraft and a second aircraft at 6502, selecting, foreach aircraft, a respective target position within the close formationand a corresponding boundary envelope encompassing each respectivetarget position at 6504, and providing flight control input for aligningthe first and second aircraft in respective initial positions within theclose formation at 6506.

FIG. 66 shows a method 6600 of changing positions of at least twoaircraft in a close formation flight in accordance with one or moreembodiments of the present invention. The method 6600 comprisesdetermining new target positions of at least leader aircraft onefollower aircraft at 6602, providing flight control input for coursealigning the leader aircraft and the follower aircraft in respectiveinitial positions within the close formation at 6604, tracking, by atleast one aircraft in the close formation, at least one vortex generatedby at least one other aircraft in the close formation at 6606, and basedon the tracking, providing flight control input to adjust a relativeposition between the leader aircraft and the follower aircraft at 6608.

FIG. 67 shows a method 6700 for metric evaluation of a close formationbetween a leader aircraft and a follower aircraft. The method 6700includes selecting a formation flight metric for evaluation of a closeformation flight at 6702, collecting data for evaluating the metric at6704, and calculating the metric using collected data at 6706.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof.

1. A method of sensing three dimensional (3D) airflow by an aircraft,comprising: collecting measurements characterizing airflow near theaircraft; analyzing the collected measurements; creating, by aprocessor, a computer model predicting one or more 3D airflow patternsparameter values based on the analyzing; obtaining one or moreadditional measurements characterizing airflow near the aircraft;evaluating an error between an airflow parameter value predicted by thecomputer model and the one or more additional measurement; and varyingat least one flight parameter of the aircraft in response to theanalyzed measurements to cause a positional change of the aircraft. 2.The method of claim 1, wherein at least some of the measurements arecollected by at least one other aircraft flying in close formation withthe aircraft.
 3. The method of claim 1, wherein at least somemeasurements are collected by a sensor array.
 4. The method of claim 3,wherein the sensor array includes at least one of a differential airflowprobe, a vane airflow probe, a hot wire probe, or a hot film probe. 5.The method of claim 1, wherein the collecting comprises measuring usinga vortex eye sensor.
 6. The method of claim 1, wherein the analyzingcomprises at least one of filtering or averaging collected measurementdata.
 7. The method of claim 6, wherein the analyzing comprises usingKalman filters to filter collected measurement data.
 8. The method ofclaim 1, wherein measurements collected during the collecting include atleast one of airflow velocity, airflow speed, airflow direction, airpressure, air temperature, or an aircraft angle of attack of theaircraft.
 9. The method of claim 1, wherein at least some measurementscollected during the collecting are derived from flight control signalsapplied to one or more control surfaces of the aircraft.
 10. The methodof claim 1, further comprising varying at least one flight parameter ofthe aircraft prior to obtaining at least one measurement of the one ormore additional measurements.
 11. The method of claim 10, wherein the atleast one flight parameter includes at least one of an aircraft angle ofattack, heading, altitude or velocity.
 12. The method of claim 1,wherein the computer model created during the creating is a 3D model ofa vortex field.
 13. The method of claim 12, wherein creating a computermodel comprises using a horseshoe vortex model.
 14. The method of claim12, wherein creating a computer model comprises using a single vortexmodel.
 15. The method of claim 12, wherein creating a computer modelcomprises modeling a relative position of a vortex eye.
 16. The methodof claim 12, wherein creating a computer model comprises modeling aflight direction toward a vortex eye.
 17. The method of claim 12,further comprising changing a relative position of the aircraft relativeto the vortex field.
 18. The method of claim 1, further includingadjusting the model based on the evaluating.
 19. A method of searchingfor an airflow pattern, comprising: defining a target search arearelative to an aircraft; establishing a dithering flight patternintersecting with the target area; collecting measurementscharacterizing airflow near the aircraft; analyzing the collectedmeasurements; and determining a location of an airflow pattern based onthe analyzing.
 20. The method of claim 19, wherein the target searcharea is defined with respect to a second aircraft.
 21. The method ofclaim 19, wherein the dithering flight pattern is maintainedcontinuously by the aircraft until sufficient data is collected tocreate a model of the airflow pattern.
 22. The method of claim 19,further comprising exchanging telemetry data with other aircraft. 23.The method of claim 19, wherein the airflow pattern is a vortexgenerated by a second aircraft.
 24. The method of claim 19, wherein thedetermining comprises using a neural network for vortex patternrecognition.
 25. The method of claim 19, wherein the determiningcomprises performing continuous vortex sensing using at least twodifferent airflow sensors.
 26. The method of claim 19, wherein thedetermining comprises performing continuous vortex sensing using aplurality of airflow sensors distributed along a spanwise direction ofan aircraft wing and positioned on stand-off booms in front of a leadingedge of the aircraft wing.
 27. The method of claim 19, wherein thedetermining comprises performing continuous vortex sensing using anairflow sensor on at least one of a fuselage of the aircraft, a tail ofthe aircraft, a tail of the aircraft, and a nose of the aircraft. 28.The method of claim 19, wherein establishing the dithering patterncomprises varying at least one flight parameter of the aircraft relativeto a second aircraft during the collecting.
 29. A method of vortextracking by an aircraft, comprising: receiving airflow data from anairflow sensor on the aircraft; analyzing the airflow data by an onboardprocessor; mapping at least a part of a vortex field by the onboardprocessor; identifying the location of a vortex core; and measuring theposition of the vortex core with respect to the aircraft.
 30. The methodof claim 29, further comprising subdividing the vortex field intodifferent vortex regions and identifying locations of respective vortexcores.